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A. H. ACKERMAN.

RESILIENT ELEMENT.

APPLICATION FILED MAY 29. 1917. RENEWED 061'. 8.1919.

1,324,440. Patented Dec. 9,1919.

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ALBERT l- ACKERYMAN, OF CLEVELAND, OHIO, ASSIGNOR TO THE ACKERMAN WHEEL COMPANY, OF CLEVELAND, DI-16, A CORPORATION OF DELAVARE.

RESILIENT ELEMENT.

Application filed May 29, 1917, Serial No, 171,641. Renewed Gctober 8, 1919.

To all whom z't may concern:

Be it knownfthat I, ALBERT H. ACKER- MAN, a citizen of the United States, and residing at Cleveland, in the county of Cuyahogaand State of Ohio, have invented a new and Improved Resilient Element, of which the following specification is a full disclo sure.

This invention deals with a heat-treated steel spring characterized by differential tempering proportioned inirelation to the variations in thickness, whereby a novel metallurgical product is obtained possessing qualities preeminently adapting it for use as a resilient element.

- Heretofore strips of steel of uniform thickness'have been tempered so as to vary gradually from one extremity toward the other, but not to vary gradually in opposite directions from an intermediate point toward its extremities. Also, tapering strips have been tempered uniformly throughout, but not variably in proportion to the taper. None of the foregoing methods will yield a tempered article suitable for certain pur poses. r

The primary object of this invention is to devise a method of tempering, in conjunction with a mode of dimensioning, such that a new article of manufacture in thenature of a resilient leaf spring will be produced capable of satisfying conditions under which the heretofore available springs have failed.

Other objects will be in part obvious from the annexed drawings and in part indicated in connection therewith by the following analysis of this invention. This invention accordingly-consists in the features of construction, combination of parts and in the unique relations of the members and in the relative proportioning and disposition thereof, all as more com: pletely outlined herein.

To enable others skilled in the art so fully to comprehend the underlying features that they may embody the same by the numerous modifications in structure and relation contemplated by this invention, drawings depicting a preferred form have been annexed as a part of this disclosure, and in such Specification of Letters Patent.

Patented Dec. 9, 1919.

Serial No. 329392.

drawings, like characters of reference; dee note corresponding partsithroughout all the views, of which: Figure l is aside elevation of a leaf spring constructed in accordance with: this method and displaying the characteristics ofthis invention. Fig.2 is: a front elevation or. said resilient element.

Continuing now by way of a moredetailed analysis, it may be explained that, for certain purposes, it is desirable to. resiliently provide for relative-movements between: a

floating element A and a base element -B; 7

these relative movements being compounded of two elemental motions, to wit: an approach of the element A toward the element B along a radial line such as. a.b, which 'may' be regarded as the normal elemental motion, and an annular displacement. between the elements A and B as indicated by the arc ccZ subtended about B as its centen This also presupposes an approach and recession, of the element A with respect to the element B along what may be termed the abnormal line of movement ed'. These elemental'motions are in turn compounded and create complex motions. In order that the motion along the are cd may be resiliently opposed, it is essential that the intervening spring member G shall be clamped rigidly vise-like at the point 1 to the base element B so as to occasion adequate proportional resistances. On the, other hand, the diversity of movements attributable to the floating element A calls for a pivotal or lOCking connection between the floating eleinent A and the intervening resilient memer C.

From the foregoing analysis, it will be perceived that the nature of fiexation of the element C is radically'diiferent at its point. of emergence 2 from the base member B than it is at the point of departure 3. fIOIll' the floating element A. In the. latter case, due to the pivotal connection, thelateral deflection is at right angles'to the lateral der fiection of the portion 4 and differs in char- As a, consequence, peculiar bending conditions obtain throughout the intervening pora of t resilient eleneut C, and the purs inventi J to so construct this that the stresses and strains will b ed in such a manner that the elenot be locally fatigued in the performanie of its functions, and yet so that the proper yielding resistances or spring actions will be secured between the members it and B.

In the development of this invention, it has been found that the spring C tends to break at the point 2 where it emerges from the base member B and at times also at other intermediate points. The investigations made for the purpose of rectifying this clifficulty have led to the development of a structure which will function properly without undue breakage even under very severe conditions of operation.

C indicates a strip of sheet steel having its root thickened and contoured, as indicated by 5, so that it may be clamped viselike in the member B, which is here shown diagrammatically for purposes of clearness. At its other end, the strip is bent around to form an eye 6 adapted to receive opposing bushings 7 and 8 which embrace the pivoted pin and minimize the wear thereof. Instead of employing a strip of uniform thickness from end to end this invention proposes one that decrementally varies in thickness from point 2 to about the region 9 and thereafter incrementally from said region to its other extremity. This physical dimensioning is obtained by employing non-circular rollers through which the metal is passed when hot and pla tie and which are so cammed to create the desired variability. At the region 9, the element may be about one-half, or even less, of the thickness at its extremity. The spring element is then subjected to a differential tempering process. It will he understood that, depending upon the particular chemical analysis of the steel employed, the absolute temperatures may vary somewhat from the following schedule, but said schedule will sufiiciently explain the principles to be followed to render the characteristics of this invention clear.

T he spring a whole is first properly annealed and is then hardened throughout by being heated uniformly to about l-l7o F. and this temper is now differentially reduced by drawing the object at difierent heats throughout its different portions. Thus, after being preliminarily heated and quenched, it at the point D raised to 1000 F; at the point E to 975 F; at the point F to 800 F.; at the point to 900 E; and the point H to 1000 F. The article is then quenched. when thus differentially heated, and it is thereby given a differential temper and a difiierential scale of hardness proportioned in relation to the variability in its dimensions. This may be manifested by the use of a sclerometer which will indicate the following scale of hardness: at D 38; at E lO;atF 51; at G4: atHBS.

From the foregoing it will be perceived that the cross-section of this spring is at a minimum where its physical hardness is at a maximum and conversely; and that a corresponding portion obtains for the intermediate point. Consequently, this element is admirably adapted to meet the conditions explained, because it minimizes the lateral flexation at the point 2, where there is a strong tendency to breakage, and it conforms freely to the pivotal action at the axis E1; the primary flexation occurring at the point 9 and thereby forming an easy outlet so-to-speak for the distortion. The temper and proportion at the point 9 is such as will provide freely for the extent of bend set up by the migrations of the point A. This is best illustrated by Fig. 1 which shows in dotted lines the way in which the bending takes place during the movement of the axis along the line a-b.

Without further analysis, the foregoing will so fully reveal the gist of this invention that others can by applying current knowledge readily adapt it for various applications without omitting certain features that, from the standpoint of the prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention, and therefore such adaptations should and are intended to be comprehended within the meaning and range of equivalency of the 100 following claims.

Having thus revealed this invention, I claim as new and desire to secure the following combinations of steps and elements, or equivalents thereof, by Letters Patent of the 105 United States 2- 1. As a new metallurgical product; a sheet metal strip of steel having a straight root and a curved tip connected therewith by an ogee curve, the thickness varying progres- 110 sively from an intermediate point both toward its tip and its root, and its hardness varying in a converse manner.

2. As a new metallurgical product; a curved strip of tempered steel progressively 115 varying in thickness and progressively varying conversely in hardness.

3. A novel metallurgical article consisting of a strip of spring-tempered steel having its root formed flat and curving therefrom in 120 one direction for a short distance and then progressively and gradually curving in the form of a large radius sweeping in the opposite direction; and terminating at its tip in an eye; said strip being thinnest about 125 midway between the eye and the point of change in the direction of curvature and progressively thickening from said thinnest portion toward its two extremities, and the temper or hardness of said strip being in inverse proportion to its thickness.

4. A novel metallurgical product in the nature of a leaf spring consisting of a bent strip of spring-tempered steel having its root formed fiat to provide a grip and then progressively and graduallycurving therefrom and terminating at its tip in an eye; the

temper of said strip being progressively varied to provide an maximum hardness toward both ends.

In witness whereof, I hereunto subscribe my name, as attested by the two subscribing witnesses. j

I ALBERT H. ACKERMAN. Witnesses V J. R. STUART, O. STOUT.

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